This invention relates to an instrument for the treatment of dental canals, the instrument comprising a tool fitted to a mandrel intended to be fixed to a rotary driving device. The invention relates in particular, but not exclusively, to a pulp-burr.
Pulp-burrs known hitherto are formed with an active part, herein called the tool constituted by, comprised of a helical wire fixed rigidly to a mandrel intended to be fitted to an arm to drivingly rotate the mandrel and wire. This drive is provided by a motor having a driving torque which is disproportionate with respect to the mechanical strength of the wire comprising the pulp-burr, the diameter, or thickness of the wire being frequently of the order of only several hundredths of a millimeter. Consequently this means that jamming of the pulp-burr immediately causes the wore comprising the tool to break.
Various factors may cause the sudden breakage of the pulp-burr or abnormal fatigue of the tool. Included amongst these factors are mainly: severe jamming of the end of the wire at the bottom of the canal, causing immediate breakage; slight jamming or jamming of very short but repeated duration, caused by the reciprocating movement of the instrument imparted by the operator and causing abnormal fatigue of the pulp-burr; very accentuated curvature of the end of the dental canal causing abnormal fatigue of the pulp-burr; use of an over-size pulp-burr with respect to the bore of the dental canal, causing breakage or abnormal fatigue; accidental or non-accidental placing of a head of the arm in an off-centre position with respect to the assumed axis of the canal.
The breakage of a pulp-burr or any other instrument for treating dental canals constitutes an incident which is frequently much more unpleasant than simply losing an instrument. Because not only does its replacement constitute a waste of time, but it is frequently necessary and sometimes difficult to extract that part of the instrument jammed in the dental canal.